In the manufacture of carbon and graphite electrodes, a premium-grade coke is typically mixed with a binder, such as coal tar pitch and extruded into cylindrical billets. Added to the mixture are optionally various extrusion aids to improve the rheological properties of the mix by acting as a plasticizer and/or to lubricate the surfaces of the extrusion equipment. Typically, the mixing occurs at a temperature of about 160.degree. C. At this temperature, for optimum results, the pitch should have a softening point in the range of 95.degree. C. to 100.degree. C. Such a pitch can be provided by adjusting the conditions of the fractionation of the coal tar or petroleum from which the pitch is derived. However, in order to increase the coking value of the pitch (the fraction of the original material ultimately converted to carbon or graphite in the final baked product), it is often the practice to use a pitch with a higher softening point, for example 110.degree. C., and add a pitch plasticizer to depress the softening point to the desired value.
Accordingly various plasticizing agents have been added to pitch. Materials that have been used as plasticizers are fatty acids, such as capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, eleostearic acid, and ricinoleic acid or mixtures thereof; as well as phenol, furfuryl alcohol, furfural, and various aromatic fractions derived from coal tar and petroleum.
After the mix is extruded, the resulting composites or green carbon bodies are baked to remove the volatile constituents and polymerize the remaining constituents to leave a substantially pure carbon body. Optionally the carbon body is further heated to convert the carbon into graphite. The properties of the baked carbon or graphite body are dependent on several factors. For example, contaminants and additives may contribute to an undesirable lowering of the density, as well as negatively influencing such properties as the coefficient of thermal expansion (CTE), the specific resistance (SR), or the strength.
It is desirable, therefore, that an additive not adversely affect these properties. For this reason it is an object of the invention to provide a plasticization additive for improving the extrusion of carbon/pitch mixtures, which does not adversely affect the physical properties of the graphite or carbon product.